Nb Doping Concentration Research Articles

Electron localization in niobium doped CaMnO3 due to the energy difference of electronic states of Mn and Nb.

The electron localization in Nb-doped CaMnO3 is analyzed in terms of the space and energy distribution of electronic states employing first-principles calculations. The energy difference of Mn 3d states and Nb 4d states makes NbO6 octahedra impede electrical conduction, so the random distribution of Nb in lattices leads to the localization of electrons near the bottom of the conduction bands. Therefore, although more carriers are introduced when Nb-doping content increases, both the electrical conductivity and absolute thermopower decrease in Nb heavy doped CaMnO3. The calculated transport properties agree well with the experimental data, supporting the analysis of localization.

Influence of Nb Doping Concentration on Bolometric Properties of RF Magnetron Sputtered Nb:TiO2−x Films

The present study directly addresses the improved bolometric properties by means of different Nb doping concentrations into TiO2−x films. The x-ray diffraction patterns do not display any obvious diffraction peaks, suggesting that all the films deposited at room temperature had an amorphous structure. A small binding energy shift was observed in x-ray photo electron spectroscopy due to the change of chemical composition with Nb doping concentration. All the device samples exhibit linear I–V characteristics, which attests to the formation of good ohmic contact with low contact resistance between the Nb:TiO2−x (TNO) film and the electrode (Ti) material. The performance of the bolometric material can be evaluated through the temperature coefficient of resistance (TCR), and the absolute value of TCR was found to be increased from 2.54% to 2.78% with increasing the Nb doping concentration. The voltage spectral density of 1/f noise was measured in the frequency range of 1–60 Hz and found to be decreased with increase of Nb doping concentration. As a result, for 1 at.% Nb-doped TNO sample exhibits improved bolometric properties towards the good infrared image sensor device.

Controlling n-type conductivity of β-Ga2O3 by Nb doping

It has been confirmed that Si, Sn, and Ge are effective n-type dopants for β-Ga2O3. This letter shows that Nb doping is also a viable method for controlling the electrical resistivity and carrier density of β-Ga2O3, corresponding to the theoretical calculations about the doping of Ga2O3 with Nb [H. Peelaers and C. G. Van de Walle, Phys. Rev. B 94(19), 4 (2016)]. β-Ga2O3 single crystals with different Nb concentrations were grown by the optical floating zone method. The electrical resistivity can be varied from 3.6 × 102 Ω cm to 5.5 × 10−3 Ω cm by increasing the Nb doping concentration, and the related free carrier concentration increases from 9.55 × 1016 cm−3 to 1.8 × 1019 cm−3. The transmittance spectra and photoluminescence spectra were measured to systematically study the optical properties of Nb-doped β-Ga2O3 single crystals. The strong absorption near the IR region in the crystals is related to the increase in conductive electrons, and the decrease in blue luminescence intensity indicates a decrease in the VO concentration induced by increasing the carrier concentration.

Heteroepitaxial growth of Cu2O films on Nb-SrTiO3 substrates and their photovoltaic properties

In this paper, p-type Cu2O thin films have been epitaxially grown on n-type semiconducting (001) oriented Nb-SrTiO3 (NSTO) substrates with different Nb doping concentration by pulsed laser deposition technique. X-ray diffraction and high resolution transmission electron microscopy reveal a cube-on-cube epitaxial relationship between Cu2O and NSTO. It is found that the deposition temperature, the thickness of Cu2O films and the Nb doping concentration of NSTO substrates have critical impact on the photovoltaic (PV) properties of the Cu2O/NSTO heterojunction devices. A maximum PV performance is observed in ITO/Cu2O/NSTO device when the deposition temperature, film thickness and Nb doping concentration of NSTO are 550°C, 76nm, and 0.7wt% NSTO, respectively. The optimized PV output corresponds to the open circuit voltage, short-circuit current density, fill factor and photovoltaic conversion efficiency about 0.45V, 1.1mA/cm2, 46% and 0.23%，respectively. This work offers an insight into the strategy for developing and designing novel optoelectronics of NSTO-based oxide heterostructures.

Correlation Between Carrier Lifetime and Photolytic Performance of Nb-Doped TiO2 Single Crystals

The hydrogen generation by the photolytic of water using the semiconductor photocatalyst attracts attention as the eco-friendly technology. Rutile TiO2 is a typical photocatalyst material because of its stability against corrosion in electrolyte.1) Nb doping to TiO2 enhances electrical conductivity and visible light absorption, and thus increases their photocatalytic performance.2, 3) One of the factors affecting the photocatalytic activity is the survival time of electrons and holes released in the photocatalyst material, i.e. the carrier lifetime.4, 5) However, there is a few report on the influence of carrier lifetime on photolytic performance for Nb-doped TiO2 single crystals. Therefore, we measured carrier lifetimes and photocurrents for TiO2single crystals with different Nb doping. The samples were Nb-doped rutile TiO2 single crystals with concentration of 0.01 wt% and 0.05 wt%. We called these samples Nb-0.01 and Nb-0.05. Both samples were polished on the (110) face, and their thickness was 0.5 mm. Carrier lifetimes of both samples were measured by microwave photoconductivity decay (μ-PCD) method. In μ-PCD, the sample was excited by a pulsed light and the conductivity was probed by reflection of 10 GHz microwave. We used a 355 nm pulsed YAG laser with injected photons of 8.5×1013 cm-2. Then we measured chopped light photocurrent-potential (I-V) measurements with the three-electrode system. The three-electrode system consisted of TiO2 electrode, Pt and a saturated calomel electrode (SCE) as working, counter and reference electrodes, respectively. Electrolyte was an aqueous solution of 1 mol/L H2SO4. The light source was a solar simulator with a power density 100 mW/cm2, and the light was mechanically chopped. Figure 1 shows μ-PCD decay curves for Nb-0.01 and Nb-0.05. The decay for Nb-0.01 was slower than that for Nb -0.05. For Nb-0.01, the carrier lifetime estimated from slopes of exponential parts was ~25 ns, which was longer than that observed for Nb-0.05. From these results, we can conclude that with higher Nb doping concentration, the carrier lifetime is shorter. Deep level formed by Nb doping would act as a recombination center of electron-hole pairs.6) Figure 2 shows chopped light I-V curves for Nb-0.01 and Nb-0.05. For Nb-0.05, the onset potential was about -1.4 V vs SCE and the photocurrent was 0.36 mA/cm2 at 1.5 V vs SCE. For Nb-0.01, the onset potential was the same as for Nb-0.05, while the photocurrent was 0.72 mA/cm2at 1.5 V vs SCE. Therefore, the photocurrent is larger for the sample with lower Nb doping concentration. From the results obtained from Fig. 1 and Fig. 2, both the carrier lifetime and the photocurrent were higher in the Nb-doped rutile TiO2single crystal with concentration of 0.01 wt%. These results suggest that carrier lifetime is increased and the photolytic performance is improved by reducing the Nb doping concentration. References 1) A. Fujishima and K. Honda, Nature 238, 37 (1972). 2) J. F. Baumard and E. Tani, J. Phys. 67, 857 (1977). 3) N. Yamada, T. Shibata, K. Taira, Y. Hirose, S. Nakao, N. Lam Huong Hoang, T. Hitosugi, T. Shimada, T. Sasaki and T. Hasegawa, Appl. Phys. 4, 045801 (2011). 4) D. Colombo and R. Bowman, J. Phys. Chem. 3654, 18445 (1996). 5) W.Choi, A. Termin, and M.R. Hoffmann, J.Phys. Chem. 98, 13669 (1994). 6) T. Miyagi, M. Kamei, I. Sakaguchi, T. Mitsuhashi and A. Yamazaki, Appl. Phys. 43, 775 (2004). Figure 1

Self-Supported Niobium Doped TiO2 Nanotubes As a Negative Electrode for Lithium-Ion Microbatteries

Thierry Djenizian, Girish D. Salian, Bon Min Koo, Christophe Lefevre, Thomas Cottineau, C. Lebouin, Alexander T. Tesfaye, Philippe Knauth, Valérie Keller Modern microelectronic devices such as backup power for computer memories, MicroElectroMechanical Systems (MEMS), medical implants, smart cards, Radio-Frequency Identification (RFID) tags and remote sensors have necessitated the development of high performance power sources at the microscale. In this context, the development of three-dimensional (3D) microbatteries forms a viable alternative to provide high volumetric energy densities to meet the demands of these devices.1 The development of nano-architectured electrodes is one of the most promising approaches to realize the 3D paradigm of microbatteries.2 Among all the potential anode materials, TiO2 nanotubes (TiO2-NTs) possess remarkable characteristics for the design of 3D Li-ion microbatteries. Self-organized nanotubular materials allow a good diffusion of Li ions in the porous structures and the 1D morphology allows an efficient charge transfer along the axis of the tube that results in a good apparent electronic conductivity of the TiO2-NTs layer when compared to a film composed of nanoparticles3, 4. Anatase TiO2 can accommodate only 0.5 Li+ per formula unit, corresponding to a theoretical capacity of 168 mAh g-1. Hence, several approaches have been investigated to improve the overall performance of TiO2-NTs for the design of high-performance Li-ion microbatteries. Doping with aliovalent ions like Niobium (Nb5+) is also a facile strategy to modify the electronic properties of titanium oxide and thereby enhance the electrochemical performance.5,6 We report the fabrication of self-supported Nb doped TiO2-NTs by anodization of Nb/Ti alloys devoid of any carbon additives or binders. An increase in the capacity of the TiO2-NTs was observed as the Nb doping concentration increased. Such a composition of 10 wt.% Nb doped TiO2-NTs (Nb10-TiO2-NTs) showed a first cycle capacity of 200 mAh.g-1 (144 µAh.cm-2) compared to pristine TiO2-NTs which gave a capacity of 115 mAh.g-1 (78 µAh.cm-2) at C/10. Galvanostatic cycling tests at various C-rates revealed the influence of Nb doping in the TiO2-NTs which is shown in Fig.1 (a) and (b). Compared to pristine TiO2-NTs, the discharge capacities of doped nanotubes are improved and almost doubled when the Nb concentration reaches 10 wt.%. Besides a good cycling behaviour at multiple C-rates, an overall capacity retention of 87 % is achieved after 100 cycles. According to Electrochemical Impedance Spectroscopy measurements, the enhanced electrochemical performance of the Nb-doped TiO2-NTs is attributed to their higher electronic conductivity. References 1) B.L. Ellis, P. Knauth, T. Djenizian, Three-Dimensional self-supported metal oxides for advanced energy storage, Adv. Mater. 26 (2014) 3368-3397. 2) J.W. Long, B. Dunn, D.R. Rolison, H.S. White, Three-Dimensional Battery Architectures, Chem. Rev., 104 (2004), 4463-4492. 3) G.F. Ortiz, I. Hanzu, T. Djenizian, P. Lavela, J.L. Tirado, P. Knauth, Alternative Li-Ion Battery Electrode Based on Self-Organized Titania Nanotubes, Chem. Mater., 21 (2009), 63-67. 4) T. Djenizian, I. Hanzu, P. Knauth, Nanostructured negative electrodes based on titania for Li-ion microbatteries , J. Mater. Chem., 21 (2011), 9925-9937. 5) Y.Wang, B. M Smarsly, I. Djerdj, Niobium Doped TiO2with Mesoporosity and Its Application for Lithium Insertion, Chem. Mater., 22 (2010), 6624–6631. 6) M. Fehse, S. Cavaliere, P. E. Lippens, I. Savych, A. Iadecola, L. Monconduit, D. J. Jones, J. Rozi`ere, F. Fischer, C. Tessierand, L. Stievano, Nb-Doped TiO2 Nanofibers for Lithium Ion Batteries, J. Phys. Chem. C, 117 (2013), 13827–13835. Figure 1

CO2-tolerance and oxygen permeability of novel cobalt-free mixed-conductor oxygen-permeable Pr0.6Sr0.4Fe1-Nb O3- membranes

Abstract A series of novel cobalt-free dense oxygen-permeable membranes of the type with Pr 0.6 Sr 0.4 Fe 1- x Nb x O 3- δ (PSFN x , x = 0–0.1) were synthesized. Subsequently, the effects of Nb-doping on the microstructure, oxygen permeability, and stability of PSFN x were studied under a pure He or CO 2 atmosphere. The structure of the material did not change in either atmospheres and its stability of the material was enhanced as the level of Nb-doping increased. For the sample with x = 0 and 0.075, carbonates and sulfates were present on the sweep side of the PSF membrane, but no impurities were detected on the sweep side of the PSFN 0.075 . In addition, the oxygen-permeation performance exhibited almost no attenuation when the Nb-doping content were 0.075. As revealed by X-ray photoelectron spectroscopy, the CO 2 resistance of the material was enhanced by reducing the basicity of PSFN x , which was induced by the substitution of Fe with Nb.

Giant strain response in 2 mol% Nb-doped (Bi0.5Na0.4K0.1)TiO3 lead-free ceramics

A series of Nb-doped (Bi0.5Na0.4K0.1)TiO3 lead-free piezoelectric ceramics were fabricated by a conventional solid-state reaction method. The X-ray diffraction patterns reveal a pure perovskite structure for all the samples. A giant strain of 0.34% is achieved at 2 mol% Nb-doping concentration, and the corresponding normalized strain $$d_{33}^*$$ reaches 625 pm V−1, which is one of the best results of the BNT-based ceramics. Complex ac impedance data indicate that only the bulk effect contributes to the resistivity. The compositionally induced disruption of long-range ferroelectric order and relaxor transition contributed to the pinched polarization loops as well as the large electric field-induced strain. The results indicate that appropriate Nb-dopant content can remarkably enhance the strain level of (Bi0.5Na0.4K0.1)TiO3 ceramics, making it a promising candidate for actuator applications.

Giant tunnelling electroresistance in metal/ferroelectric/semiconductor tunnel junctions by engineering the Schottky barrier

Recently, ferroelectric tunnel junctions have attracted much attention due to their potential applications in non-destructive readout non-volatile memories. Using a semiconductor electrode has been proven effective to enhance the tunnelling electroresistance in ferroelectric tunnel junctions. Here we report a systematic investigation on electroresistance of Pt/BaTiO3/Nb:SrTiO3 metal/ferroelectric/semiconductor tunnel junctions by engineering the Schottky barrier on Nb:SrTiO3 surface via varying BaTiO3 thickness and Nb doping concentration. The optimum ON/OFF ratio as great as 6.0 × 106, comparable to that of commercial Flash memories, is achieved in a device with 0.1 wt% Nb concentration and a 4-unit-cell-thick BaTiO3 barrier. With this thinnest BaTiO3 barrier, which shows a negligible resistance to the tunnelling current but is still ferroelectric, the device is reduced to a polarization-modulated metal/semiconductor Schottky junction that exhibits a more efficient control on the tunnelling resistance to produce the giant electroresistance observed. These results may facilitate the design of high performance non-volatile resistive memories.

Fabrication and photovoltaic performance of niobium doped TiO2 hierarchical microspheres with exposed {001} facets and high specific surface area

The niobium doped hierarchical anatase TiO2 microspheres, which are consist of a serried nano-thorns and plicate nano-ribbons with exposed {001} facets, were synthesized using hydrothermal method followed by heat treatment. The effects of niobium on the microstructures and photovoltaic performances of the dye-sensitized solar cells (DSSCs) were studied. The results revealed that Nb5+ doping replaces Ti4+ cations in TiO2 lattice, and the bandgap of the films varies with increasing Nb doping concentration because of the downshift of the conduction band minimum (CBM). The niobium-doped TiO2 DSSCs with moderate loadings show enhanced performance comparing with their pure TiO2 counterparts. Optimally, the conversion efficiency of the Nb-3.5 (Nb 3.5mol%) DSSC is 4.99%. This is higher than that (4.39%) of pure TiO2 cells by 13.7%. This is due to the fact that the Nb-doped solar cells have increased the number of the photo-induced electrons because of their exposed (001) facets and higher specific surface area; and enhanced electrons collection and transport because of the downshifted CBM of the Nb-doped TiO2. However, heavy Nb doping results in the decrease of the performance of the niobium-doped cells due to the excessive defects within the Nb-TiO2 samples resulting in enhanced charge recombination at defects.

Effect of Nb Doping on Chemical Sensing Performance of Two-Dimensional Layered MoSe2.

Here, we report that Nb doping of two-dimensional (2D) MoSe2 layered nanomaterials is a promising approach to improve their gas sensing performance. In this study, Nb atoms were incorporated into a 2D MoSe2 host matrix, and the Nb doping concentration could be precisely controlled by varying the number of Nb2O5 deposition cycles in the plasma enhanced atomic layer deposition process. At relatively low Nb dopant concentrations, MoSe2 showed enhanced device durability as well as NO2 gas response, attributed to its small grains and stabilized grain boundaries. Meanwhile, an increase in the Nb doping concentration deteriorated the NO2 gas response. This might be attributed to a considerable increase in the number of metallic NbSe2 regions, which do not respond to gas molecules. This novel method of doping 2D transition metal dichalcogenide-based nanomaterials with metal atoms is a promising approach to improve the performance such as stability and gas response of 2D gas sensors.

Dynamically tuning near-infrared-induced photothermal performances of TiO2 nanocrystals by Nb doping for imaging-guided photothermal therapy of tumors.

Conventional wide bandgap semiconductors can absorb UV/visible light but have no photoabsorption band in the near-infrared (NIR) region, leading to difficulty in their use as NIR-responsive agents. With TiO2 as an example, we report the tuning from UV-responsive TiO2 nanocrystals to blue TiO2 nanocrystals with newly appeared NIR absorption band through the Nb-doping strategy. A strong NIR band should result from the localized surface plasmon resonances due to the considerable free electrons originating from the efficient incorporation of Nb5+ ions (<15.5%). Interestingly, under the irradiation of a 1064 nm laser, Nb-doped TiO2 nanocrystals can convert laser energy into heat, and higher Nb-doping content can lead to higher NIR-induced temperature elevation, highlighting that the photothermal performances of TiO2 nanocrystals can be dynamically modulated by adjusting the Nb-doping levels. After coating with PEGylated phospholipid, the resulting nanocrystals display water dispersibility, high photothermal conversion efficiency and cytocompatibility. Therefore, these Nb-doped TiO2 nanocrystals can be used as efficient and heavy-metal-free nanoagents for the simultaneous NIR/photoacoustic imaging and photothermal therapy of tumors using a 1064 nm laser in the second biological window.

Effect of Nb and more Fe ions co-doping on the microstructures, magnetic, and piezoelectric properties of Aurivillius Bi5Ti3FeO15 phases

Aurivillius Bi5Ti3−2xFe1+xNbxO15 (BTFNO, x = 0.1, 0.2, 0.3, and 0.4) phases were prepared by solid state reaction method. The structures and dielectric responses were studied, and especially the effects of Nb with a higher valence and more Fe co-doping on the magnetic and piezoelectric properties were addressed in detail. The BTFNO samples were well crystallized with no detectable impurities, and plate-like microstructures with various sizes demonstrate the typical characteristics of bismuth-layer Aurivillius materials. It is found that a dielectric loss peak appears in the Nb and Fe co-doped Bi5Ti3FeO15 (BTFO) ceramics, and it has a shift towards a lower frequency with increasing the Nb doping contents. Furthermore, antiferromagnetic long-range magnetic order is improved with the introduction of Nb and more Fe co-doping. And compared with that of the parent BTFO forms, a clear discrepancy, which is indicative of a super-paramagnetic behavior, of the magnetization vs. temperature curves in zero-field cooling and field cooling cases is observed by the introduction of the Nb and more Fe ions. More interestingly, the introduction of Nb and more Fe ions can suppress the preferred c-axis growth while promoting the a-/b-axis growth of the plate-like grains, and thus favors the piezoelectric behaviors of the BTFO Aurivillius phases along the growth orientation.

Structural, optical and electrical investigations on Nb doped TiO2 radio-frequency sputtered thin films from a powder target

Pure and Nb doped TiO2 (TNO) thin films were deposited onto glass substrates by RF magnetron sputtering technique using a Nb and TiO2 mixture powder target at room temperature to explore the possibility of producing sputtered TNO films by a low cost process. The effect of Nb doping on the structure, morphology, optical and electrical properties of the prepared films was studied by systematically varying the Nb content from 2 to 6 wt%. GXRD results show that the deposited films mainly possess rutile phase with the (110) orientation. Raman spectra confirm that the deposited films are predominantly rutile phase. Surface roughness increases with the increase of Nb doping concentration , which may be attributed to the structural changes in the film due to the incorporation of Nb into the TiO2 lattice. Optical transmittance in the visible range reaches 85 % for the undoped films then it decreases as the doping content increases. Doping by niobium resulted in a slight increase in the optical band gap energy of the films due to the Burstein–Moss effect. The resistivity measurement of TNO films reveals that the Nb doping improves the electrical conductivity of the deposited films compared to the undoped one. The best value was observed for films deposited at 4 wt% Nb.

Defect Complex Effect in Nb Doped TiO2 Ceramics with Colossal Permittivity

Donor-doped Nb x Ti1−x O2 (x = 1%, 2%, 4%, 6%, and 8%) ceramics with giant permittivity (>104) and a very low dielectric loss (∼0.05) were sintered under flowing N2 at 1400°C for 10 h. By increasing Nb doping concentration, two different dielectric responses were evidenced in the frequency dependence of dielectric properties of Nb doped TiO2 ceramics, which corresponded to the space charge polarization and the electron-pinned defect-dipoles effect, respectively. Especially, combined with the x-ray photoelectron spectroscopy results, the electron-pinned defect-dipoles induced by the $$2({\hbox{Nb}}^{5 + } )_{\rm{Ti}}^{ \bullet } \to 4({\hbox{Ti}}^{3 + } )^{\prime}_{\rm{Ti}} \leftarrow {\hbox{V}}_{\rm{o}}^{ \bullet \bullet }$$ defect complex were further confirmed to give rise to both their high er and low tan δ in the high frequency range for the Nb x Ti1−x O2 ceramics with x > 4%.

Electronic structures and optical properties of Nb-doped SrTiO3 from first principles**Project supported by the National Natural Science Foundation of China (No. 10974077) and the Innovation Project of Shandong Graduate Education, China (No. SDYY13093).

The n-type Nb-doped SrTiO3 with different doping concentrations were studied by first principles calculations. The effects of Nb concentration on the formation enthalpy, electronic structure and optical property were investigated. Results show that Nb preferentially enters the Ti site in SrTiO3, which is in good agreement with the experimental observation. The Fermi level of Nb-doped SrTiO3 moves into the bottom of the conduction band, and the system becomes an n-type semiconductor. The effect of Nb-doping concentration on the conductivity was discussed from the microscopic point of view. Furthermore, the 1.11 at% Nb-doped SrTiO3 shows strong absorption in the visible light and becomes a very useful material for photo-catalytic activity. The 1.67 at% and 2.5 at% Nb-doped models will be potential transparent conductive materials.

Microstructure and electric properties of Nb doping x(Ba0.7Ca0.3)TiO3–(1−x)Ba(Zr0.2Ti0.8)O3 ceramics

In this paper, t mol% Nb2O5 doped x(Ba0.7Ca0.3)TiO3–(1−x)Ba(Zr0.2Ti0.8)O3 [xBCT–(1−x)BZT–t mol% Nb2O5] lead-free piezoelectric ceramics were prepared successfully using a solid-state reaction technique. Firstly, the phase transition of xBCT–(1−x)BZT ceramics were investigated, and it was found that 0.47BCT–0.53BZT sample shows a rhombohedral (R)–tetragonal (T) phase transition at room temperature near Morphotropic Phase Boundary and presents better ferroelectric and piezoelectric properties compared with the other component ceramics. On this basis, the crystal structure, surface morphologies and electrical properties of the Nb2O5 doped 0.47BCT–0.53BZT ceramic were studied in detail. It was found the grain size increases monotonously and the microstructure become more denser and homogeneous when Nb-doping concentration increases above t = 0.3, and a maximum strain value of 0.132% was obtained at E = 20 kV/cm. Additionally, the excellent electric properties with a high remanent polarization (Pr = 8.3 μC/cm2), a low coercive field (Ec = 1.55 kV/cm) were also obtained on 0.47BCT–0.53BZT–0.3 mol% Nb2O5 lead-free ceramics, which is promising for application in lead-free practical applications.

Highly conductive Nb doped BaSnO3 thin films on MgO substrates by pulsed laser deposition

Ba(NbxSn1-x)O3 (BNSO) films were epitaxially grown on (001) oriented MgO substrates with Nb doping content from 0.00 to 0.15 by pulsed laser deposition. The structural, electrical, and optical properties of the films were investigated in detail by x-ray diffraction, x-ray photoelectron spectroscopy, Hall effect and transmittance spectroscopy. The lowest room temperature resistivity value of 4.81 × 10−4 Ω cm with carrier concentration and mobility of 6.59 × 1020/cm3 and 19.65 cm2/V was observed in the film at x = 0.05, indicating an excellent electrical conductivity. All the BNSO films exhibit a high transmittance of more than 80% in the visible range. The variation of band gap Eg with Nb doping content was interpreted by the Burstein-Moss effect and the occurrence of octahedral tilt distorting. Excellent optical and electrical properties suggest that BNSO films have potential applications in the optoelectronic devices as transparent and conducting oxide material.

Doping concentration effects upon column-structured Nb:TiO2 for transparent conductive thin films prepared by a sol–gel method

The column-structured Nb-doped TiO2 (TNO) films with various Nb concentrations in the range between 0 and 10 at.% have been prepared by a sol–gel method. The phase compositions, element concentrations, microstructures, and optical-electron properties have been characterized by using X-ray diffraction, X-ray photoelectron spectroscopy, electron microscopy, and UV/Vis/Near-IR spectrophotometer. The experimental results show that all of the samples prepared in the present work exhibit column-structured morphology and Nb doping concentration has a non-monotonic effect upon the microstructure. The relatively low conductivity and high transmittance of the samples demonstrate that column-structured microstructures greatly improve the optical and electronic properties of TNO films. The favorable sample with 10 at.% Nb doping concentration exhibits a resistance of about 2.27 Ω cm and transmittance of approximately 68.78% with 85 nm thickness.

Anomalous behavior of B1g mode in highly transparent anatase nano-crystalline Nb-doped Titanium Dioxide (NTO) thin films

The effect of Niobium doping and size of crystallites on highly transparent nano-crystalline Niobium doped Titanium Dioxide (NTO) thin films with stable anatase phase are reported. The Nb doping concentration is varied within the solubility limit in TiO2 lattice. Films were annealed in controlled environment for improving the crystallinity and size of crystallites. Elemental and thickness analysis were carried out using Rutherford backscattering spectrometry and cross sectional field emission scanning electron microscopy. Structural characteristics reveal a substitutional incorporation of Nb+5 in the TiO2 lattice which inhibits the anatase crystallites growth with increasing the doping percentage. The micro-Raman (MR) spectra of films with small size crystallites shows stiffening of about 4 cm−1 for the Eg(1) mode and is ascribed to phonon confinement and non-stoichiometry. In contrast, B1g mode exhibits a large anomalous softening of 20 cm−1 with asymmetrical broadening; which was not reported for the case of pure TiO2 crystallites. This anomalous behaviour is explained by contraction of the apical Ti-O bonds at the surface upon substitutional Nb5+ doping induced reduction of Ti4+ ions also known as hetero-coordination effect. The proposed hypotheses is manifested through studying the electronic structure and phonon dynamics by performing the near edge x-ray absorption fine structure (NEXAFS) and temperature dependent MR down to liquid nitrogen temperature on pure and 2.5 at.% doped NTO films, respectively.